Particle image velocimetry investigation of a turbulent boundary layer manipulated by spanwise wall oscillations

Cicca, Gaetano Maria Di; Iuso, Gaetano; Spazzini, Pier Giorgio; Onorato, Michele

doi:10.1017/s002211200200157x

Cited by 64 publications

(43 citation statements)

References 31 publications

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“…3 , Choi et al 4 , Choi 5 , Di Cicca et al 6 and Ricco 7 all show a qualitatively similar response to oscillatory wall motion, downstream of a stretch of around 3-5 boundary-layer thicknesses within which the drag reduces towards its equilibrium level. However, substantial differences in the maximum drag-reduction margins are reported -ranging from 23%, measured by Ricco 7 , up to 45%, obtained by Choi and Graham 8 -and this variability reflects (if experimental errors are presumed modest) significant differences in the wall-velocity amplitude, the Reynolds numbers and also the actuation periods among the studies.…”

Section: Introductionmentioning

confidence: 85%

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The streamwise drag-reduction response of a boundary layer subjected to a sudden imposition of transverse oscillatory wall motion

Lardeau

Leschziner

2013

Physics of Fluids

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A DNS study is presented, which examines the response of a spatially developing boundary layer to oscillatory spanwise wall motion imposed over a limited streamwise stretch. At the heart of the study is the dependence of the streamwise variations in skin friction and turbulence properties on the period of the oscillatory motion, with particular emphasis placed on the behaviour downstream of the start of the actuation. The friction Reynolds number just upstream of the actuation is Re τ = 520, and the wall-scaled actuation period, T + = T u τ 2 /ν, covers the range 80-200. In contrast to channel flow, the present configuration allows the processes during the transition stretch from the unactuated state to the low-drag state and the recovery from the low-drag state to be studied. Attention focuses primarily on the former. Results are included for the time-averaged turbulent stresses, their budgets and PDFs, as well as a range of phase-averaged properties. The study brings out, for low-drag conditions, a number of features and processes that are common with those in actuated channel flow, but suggests that the maximum drag-reduction margins are lower than those in equivalent channel flow, and that the optimum actuation period is significantly shorter. The transition to the low-drag state occurs over about 5 boundary-layer thicknesses, and is characterized by substantial oscillations in all phase-averaged properties. These oscillations, provoked at the start of the spanwise motion, propagate convectively as waves and decay as the low-drag state is approached. The interactions contributing to the oscillations are discussed as part of the analysis of phase-averaged quantities.

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Section: Introductionmentioning

confidence: 85%

“…A review of the pertinent literature up to 2012 is included in a recent paper by Touber and Leschziner 2 , and another summarizing work prior to 2003 is given in Karniadakis and Choi 14 . Studies investigating fundamental interactions from a variety of viewpoints -among them Di Cicca et al 6 , Laadhari et al…”

Section: Introductionmentioning

confidence: 99%

The streamwise drag-reduction response of a boundary layer subjected to a sudden imposition of transverse oscillatory wall motion

Lardeau

Leschziner

2013

Physics of Fluids

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“…Quadrio & Ricco (2004); Ricco & Quadrio (2008); Quadrio et al (2009) ;Touber & Leschziner (2012)) and for spatially evolving boundary layers (e.g. Choi (2002);Di Cicca et al (2002); Ricco (2004); Skote (2013) ;Lardeau & Leschziner (2013)) demonstrate that the imposition of spanwise oscillatory wall motion onto a streamwise turbulent near-wall layer results in a substantial decline in skin friction if the wall-velocity amplitude and oscillation period are chosen judiciously. In the case of streamwise-homogeneous wall motion, the skin friction drops by a maximum of around 35% at the friction Reynolds number Re τ = O(200), a wall-velocity amplitude W m + = W m /u τ = 12 and oscillation period T + = T u 2 τ /ν ≈ 100, but this margin appears to decrease roughly in proportion to Re −0.2 τ , a rate based on simulations by Touber & Leschziner (2012) at Re τ = 500 and 1000.…”

Section: Introductionmentioning

confidence: 99%

Spanwise oscillatory wall motion in channel flow: drag-reduction mechanisms inferred from DNS-predicted phase-wise property variations at

2014

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A DNS-based study is presented, which focuses on the response of near-wall turbulence and skin friction to the imposition of an oscillatory spanwise wall motion in channel flow.One point of contrast to earlier studies is the relatively high Reynolds number of the flow, namely Re τ =1000. Another is the focus on transients in the drag that are in the form of moderate oscillatory variations in the skin friction and near-wall turbulence around the low-drag state at a sub-optimal actuation period. These conditions allow phase-averaged statistics to be extracted, during the periodic drag decline and rise, that shed light on the interaction between turbulence and the unsteady Stokes strain. Results are presented for, among others, the phase-averaged second-moments of stochastic fluctuations and their budgets, enstrophy components and joint PDFs. The study identifies velocity skewnessthe wall-normal derivative of the angle of the velocity vector -as playing a significant role † Email address for correspondence: l.agostini@imperial.ac.uk 2 L. Agostini, E. Touber and M. A. Leschzinerin the streak-damping process during the drag-reduction phase. Furthermore, the phasewise asymmetry in the skewness is identified as the source of a distinctive hysteresis in all properties, wherein the drag decline progresses over a longer proportion of the actuation cycle than the drag increase. This feature, coupled with the fact that the streakgeneration time scale limits the ability of the streaks to re-establish themselves during the low-skewness phase when the actuation period is sufficiently short, is proposed to drive the drag-reduction process. The observations in the study thus augment a previously identified mechanism proposed by two of the present authors, in which the drag-reduction process was linked to the rate-of-change in the Stokes strain in the upper region of the viscous sublayer where the streaks are strongest. Furthermore, an examination of the stochastic-stress budgets and the enstrophy lead to conclusions contrasting those recently proposed by other authors, according to which the drag-reduction process is linked to increases in enstrophy and turbulence-energy dissipation. It is shown, both for the transient drag-reduction phase and the periodic drag fluctuations around the lowdrag state, that the drag decrease/increase phases are correlated with decreases/increases in both enstrophy and dissipation.

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“…A similar analysis was also carried out on a set of experimental data [15] for a boundary layer flow. These data are contained in 596 files, each consisting a single window of data including the values of two velocity components in a plane parallel to the wall in a grid of 59 × 59 nodes.…”

Section: Filtrationmentioning

confidence: 99%

Analysis of data on the relation between eddies and streaky structures in turbulent flows using the placebo method

Chernyshenko¹,

Cicca²,

Iollo³

et al. 2006

Fluid Dyn

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-An artificially synthesized velocity field with known properties is used as a test data set in analyzing and interpreting the turbulent flow velocity fields. The objective nature of this approach is utilized for studying the relation between streaky and eddy structures. An analysis shows that this relation may be less significant than is customarily supposed.Keywords: turbulence, visualization, streaky structures, eddy, Galilean decomposition.Until recently it was generally accepted that the existence of so-called streaky structures in turbulent wall flows was dictated by the presence of eddy structures [1]. Now it has been shown [2] that in reality the streaky structures develop regardless of the eddy structures, since the approach which involves rejecting the assumption of a relation between the eddy and streaky structures gives extensive qualitative and quantitative results that are consistent with the experiments. At the same time, over several decades in both physical and numerical experiments the data usually interpreted as proof of the relation between streaky and eddy structures were collected. In the light of the results of [2] the existence of these data can be explained in two ways. We can assume that the streaky structures, which do not themselves depend on the eddy structures, cause the eddies thus leaving on them the imprint of their structure. The second possibility is that the generally accepted interpretation of the data is erroneous. In fact, modern eddy identification techniques were developed under conditions in which the presence of a relation between the streaky structures and eddies was assumed to be so obvious that identification methods which did not confirm this relation could be rejected as necessarily ineffective.The present study represents an attempt to determine which of these two possibilities is the more likely. For this purpose a placebo is constructed, that is a velocity field resembling a turbulent one with streaky structures and eddies but such that the streaky structures and the rest of the field are definitely not interrelated. Then the placebo and samples of real turbulent velocity fields are processed using the same methods and the results are compared.

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Particle image velocimetry investigation of a turbulent boundary layer manipulated by spanwise wall oscillations

Cited by 64 publications

References 31 publications

The streamwise drag-reduction response of a boundary layer subjected to a sudden imposition of transverse oscillatory wall motion

The streamwise drag-reduction response of a boundary layer subjected to a sudden imposition of transverse oscillatory wall motion

Spanwise oscillatory wall motion in channel flow: drag-reduction mechanisms inferred from DNS-predicted phase-wise property variations at

Analysis of data on the relation between eddies and streaky structures in turbulent flows using the placebo method

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